Effect of Microstructure on the Cycling Behavior of Li–In Alloy Anodes for Solid-State Batteries

Abstract

Indium−lithium alloys operating in the two-phase region of indium metal and the InLi intermetallic are the counter and reference electrodes of choice in two-electrode solid-state batteries. At high current densities on both charge and discharge, they offer low polarization, good accessible capacity, and good cycle life. By synthesizing a phase pure InLi intermetallic and measuring its diffusion and mechanical properties, it is clear that the electrochemical performance is attributable to measured fast diffusion kinetics in the InLi intermetallic, D Li 298K = 5.5 × 10 −7 cm 2 s −1 . The indium metal phase is essentially ion-blocking, so the performance is tied to the microstructure, which evolves with cycling. A simple two-layer microstructure is proposed, based on the fundamental understanding established, which maximizes performance. Despite the limitations of indium-based alloys in commercial applications, the lessons learned can be extended to other fast-conducting lithium intermetallics.

Electrochemical behavior of elemental alloy anodes in solid-state batteries

“…Any internal surface area, such as cracks or pores, created by the volume change of the foils remains unexposed to the SSE, which significantly reduces the extent of SEI formation compared to liquid electrolytes. ,, Generally, lithium alloy materials have good chemical compatibility with SSEs due to their higher alloying potentials than lithium metal, , which also mitigates dendritic growth of lithium due to the lack of lithium deposition . Alloy foil anodes in SSBs have been investigated mainly in their prelithiated forms, or with modified microstructure. ,− Indium and physically alloyed lithium–indium foils are commonly used as anodes in laboratory SSB cells because of their simple fabrication, constant potential during alloying/dealloying, and stable cycling performance. ,− Abundant and cost-effective aluminum foils are particularly attractive beyond indium because of the possibility to attain high specific energy/energy density comparable to that of SSBs with dense silicon anodes . Recent reports on aluminum-based anodes have shown stable cycling in SSBs by forming Al–In multiphase microstructures and LiAl alloys. − Silver and magnesium foils have also been widely employed to form lithium-rich solid solution alloys, which minimizes lithium dendrite growth and contact loss at the SSE/electrode interface. − Despite the growing use of alloy foil anodes in SSBs, the reaction mechanisms and degradation behavior of the range of elemental materials that can alloy with lithium are not well understood compared to within lithium-ion batteries with liquid electrolytes.…”

“… 16 Alloy foil anodes in SSBs have been investigated mainly in their prelithiated forms, or with modified microstructure. 11 , 17 − 29 Indium and physically alloyed lithium–indium foils are commonly used as anodes in laboratory SSB cells because of their simple fabrication, constant potential during alloying/dealloying, and stable cycling performance. 11 , 17 − 21 Abundant and cost-effective aluminum foils are particularly attractive beyond indium because of the possibility to attain high specific energy/energy density comparable to that of SSBs with dense silicon anodes.…”

“… 11 , 17 − 29 Indium and physically alloyed lithium–indium foils are commonly used as anodes in laboratory SSB cells because of their simple fabrication, constant potential during alloying/dealloying, and stable cycling performance. 11 , 17 − 21 Abundant and cost-effective aluminum foils are particularly attractive beyond indium because of the possibility to attain high specific energy/energy density comparable to that of SSBs with dense silicon anodes. 3 Recent reports on aluminum-based anodes have shown stable cycling in SSBs by forming Al–In multiphase microstructures and LiAl alloys.…”

Intimate Protective Layer via Lithiation Sintering for All-Solid-State Lithium Metal Batteries

“…These characteristics enable the stable and efficient operation of Li metal anodes under high current densities. Various alloy metals, including indium (In), − silver (Ag), − silicon (Si), aluminum (Al), and magnesium (Mg), , have been explored for use as protective layers or host materials. These metals exhibit the potential to function as lithium-ion conductors, featuring remarkable Li ion diffusion coefficients achieved by alloying with Li metals. − Among these options, the Li-Si alloy stands out due to its exceptionally high Li concentration and superior electrochemical stability with SE, making it a promising candidate. − Despite its potential physicochemical properties, the effective Li-Si alloy protective layer in ASSLMBs has not yet been developed because the formation of uniform protective layers over large areas is challenging due to the limited electrochemical lithiation of Si particles …”